What are electron deficient compounds? Are BCl3 and SiCl4 electron deficient species? Explain.

Electron deficient compounds are molecules that possess fewer electrons than what is typically expected based on the octet rule or the duet rule in the case of hydrogen. These compounds often exhibit incomplete valence electron shells and tend to be highly reactive, seeking to gain electrons to achieve a more stable electronic configuration.

BCl3 (boron trichloride) and SiCl4 (silicon tetrachloride) are indeed examples of electron deficient species. Let's examine each:

1. BCl3 (boron trichloride):

   • Boron has three valence electrons, and in BCl3, it forms three covalent bonds with chlorine atoms.
   • However, boron itself only has six electrons around it, leaving it short of the octet rule. Thus, BCl3 is electron deficient.
   • Due to its electron deficiency, BCl3 is highly reactive and acts as a Lewis acid, readily accepting a pair of electrons from a Lewis base.

2. SiCl4 (silicon tetrachloride):

   • Silicon has four valence electrons, and in SiCl4, it forms four covalent bonds with chlorine atoms.
   • Similar to boron, silicon ends up with only eight electrons around it, which is still short of a complete octet.
   • Therefore, SiCl4 is also electron deficient.
   • Silicon tetrachloride is also reactive due to its electron deficiency, though it's not as reactive as boron trichloride.

In both cases, the central atom (boron or silicon) lacks a full complement of valence electrons, making these molecules electron deficient. This electron deficiency makes them susceptible to reacting with species that can donate electron pairs, making them important reagents in various chemical processes.